The present invention relates to a macro lens system, and more particularly to a photographic lens system that is relatively bright as expressed by an F-number of about 2.8 and enables every object from the object at infinity to a substantially life-size object to be continuously photographed.
So far, lenses capable of focusing on closer objects (close-up photography) have generally been designed such that aberrations at about 1/10 can be predominantly corrected. For this reason, such lenses are still less satisfactory in terms of correction of aberrations at infinity than ordinarily used camera lenses. Among means known to solve this problem, there is a so-called floating mechanism wherein the air space between the respective lens groups is varied during focusing, thereby compensating for degradation of aberrations.
Some outcome has been accomplished by such a floating mechanism. However, this mechanism, although enabling spherical aberration, coma and the like to be well corrected, is still likely to give rise to some considerable variation of astigmatism and curvature of field. In particular, a noticeable field tilt on the object side often occurs, and this makes it difficult to obtain satisfactory performance over a range from the center to edge of the image plane.